Sima Yi (; ; 179 CE7 September: "Eighth month. On the day wu-yin (Sept. 7), Sima Yi, the Lord Xuan-Wen of Wu-Yang, died." 251 CE), courtesy name Zhongda, was a Chinese military general, politician, and regent of the state of Cao Wei during the Three Kingdoms period of China.
He formally began his political career in 208 under the Han dynasty's Imperial Chancellor Cao Cao,: "When Sima Yi was young he was already intelligent, and he had ambitious plans. Cui Yan said to his elder brother Sima Lang, "Your young brother has a clear intelligence and a keen sense of justice, firm decision and exceptional bravery. You are not so good as that!" Cao Cao heard about this and appointed Sima Yi to office, but Sima Yi sought to excuse himself on the grounds that he had rheumatism. Cao Cao was angry and was going to have him arrested. Sima Yi was frightened and took the post."Rafe de Crespigny notes: "Sima Yi, known by his honorary posthumous title as Emperor Xuan of Jin, was the founder of the imperial fortunes of his family, and destroyer of the Cao dynasty of Wei. There is thus a certain irony in the story that he had to be dragooned by Cao Cao into service; and it may be too good to be true." and was quickly promoted to higher office. His success in handling domestic and military affairs such as governance and the promotion of agriculture, serving as an adviser, repelling incursions and invasions led by Shu and Wu forces, speedily defeating Meng Da's Xincheng Rebellion, and conquering the Gongsun-led Liaodong commandery, garnered him great prestige. He is perhaps best known for defending Wei from a series of invasions that were led by Wei's rival state Shu between 231 and 234.
In 239, along with another co-regent Cao Shuang, he was made to preside as a regent for the young Cao Fang after the death of latter's adoptive father, Cao Rui. Although amicable at first, the relationship soon deteriorated in light of Cao Shuang's corruption, extravagance, and attempts to curtail Sima Yi's political influence. In February 249, after carefully planning and building up support, Sima Yi ousted Cao Shuang from power in a coup d'état and had him and his associates executed.
Afterwards, Sima Yi became the primary authority in Wei, although in June 251 he faced some opposition from Wang Ling's rebellion, which he swiftly dealt with. Sima Yi died on 7 September 251, at the age of 71 or 72, and was succeeded by his eldest son Sima Shi.
For the remainder of Wei's history, state power was increasingly vested in the Sima clan, which led to the establishment of the Jin dynasty, which was founded by Sima Yi's grandson Sima Yan in February 266. After Sima Yan became emperor, he honoured his grandfather with the posthumous title Emperor Xuan of Jin and the temple name Gaozu. He was also the last common ancestor of all emperors of the Jin dynasty; while emperors of the Western Jin descended from Sima Zhao (his son with wife Zhang Chunhua), emperors of the Eastern Jin descended from Sima Zhou (his son with concubine Lady Fu).
Family background
Sima Yi's ancestral home was in Xiaojing (), Wen County, Henei Commandery. His ancestor was Sima Ang the King of Yin (), who briefly ruled one of the Eighteen Kingdoms during the transition period from the Qin dynasty to the Western Han dynasty before Liu Bang's general Han Xin conquered his territory, capturing Sima Ang and his capital city Zhaoge. In the early Han dynasty, Sima Ang's former kingdom, which was largely situated in Henei, became a commandery of the Han Empire and his descendants had lived there since.: "楚漢間，司馬卬為趙將，與諸侯伐秦。秦亡，立為殷王，都河內。漢以其地為郡，子孫遂家焉。""During the Chu-Han transition [206–202 BC], Sima Ang served Zhao as a general and participated with the various lords to attack Qin. When Qin had been destroyed, he was established as King of Yin with Henei as capital [in 206 BC]. Han made the land into a commandery. [Sima Ang's] descendants made their homes there."
Sima Jūn (), an eighth-generation descendant of Sima Ang and the great-great-grandfather of Sima Yi, served as a general of the Han Empire, holding the position General Who Conquers the West ().: "自卬八世，生征西將軍鈞，字叔平。""After eight generations was born the General who Conquers the West [zhengxi jiangjun], Jun, courtesy name Shuping." Sima Jūn's son Sima Liang () held the position Grand Administrator of Yuzhang,: "鈞生豫章太守量，字公度。""Jun begat Liang, the Grand Administrator of Yuzhang, courtesy name Gongdu." and Sima Liang's son Sima Jùn () served as Grand Administrator of Yingchuan.: "量生潁川太守儁，字元異。""Liang begat Jùn, the Grand Administrator of Yingchuan, courtesy name Yuanyi." Sima Jùn's son Sima Fang served as the Prefect of Luoyang (), Intendant of Jingzhao, and later as Cavalry Commandant () towards the end of the Eastern Han dynasty. Sima Yi was Sima Fang's second son.: "儁生京兆尹防，字建公。帝即防之第二子也。""Jùn begat Fang, the Intendant of Jingzhao, courtesy name Jiangong. Emperor Xuan of Jin [Sima Yi] was Fang's second son."
Sima Yi had one elder brother Sima Lang (Boda) and six younger brothers. The eight Sima brothers were collectively known as the "Eight Das" because their courtesy names all ended with da ().: 安平獻王孚字叔達，宣帝次弟也。初，孚長兄朗字伯達，宣帝字仲達，孚弟馗字季達，恂字顯達，進字惠達，通字雅達，敏字幼達，俱知名，故時號為「八達」焉。"
Early life Sima Yi displayed intelligence and great ambitions at a young age. He was knowledgeable and well-versed in Confucian classics. When chaos broke out in China towards the End of the Han dynasty, Sima Yi often expressed sympathy and concern for the people. Before he reached adulthood around the age of 19, Sima Yi once met Yang Jun, a commandery administrator who was known for spotting talents. Yang Jun described him as an "extraordinary talent". Cui Yan, a friend of Sima Yi's elder brother, Sima Lang, once said: "(Sima Yi) is intelligent, decisive, and unique. (Sima Lang) can't be compared to him.": "少有奇節，聰朗多大略，博學洽聞，伏膺儒教。漢末大亂，常慨然有憂天下心。南陽太守同郡楊俊名知人，見帝，未弱冠，以為非常之器。尚書清河崔琰與帝兄朗善，亦謂朗曰：「君弟聰亮明允，剛斷英特，非子所及也。」"
Sima Yi and his family used to live in the imperial capital, Luoyang, where his father, Sima Fang, served as a government official. Sima Yi was raised in a strict Confucian manner: He was not allowed to visit his father unless summoned, to speak to his father without being explicitly addressed, and neither was he allowed to be seated in the same room as his father.Sima Biao, Xuzhuan: "All of his sons, though they were capped and adults, if they were not ordered "go forward" they did not dare go forward, if they were not ordered "sit" they did not dare sit, and if they were not directed to be heard they did not dare speak. The solemness between father and son was like this. In 190, when the warlord Dong Zhuo dominated the Han central government and wanted to relocate the imperial capital to Chang'an, Sima Fang ordered Sima Lang to bring the Sima family out of Luoyang and return to their ancestral home in Wen County, Henei Commandery. Some months later, as Sima Lang foresaw that chaos would break out in Henei Commandery, he relocated his family to Liyang Commandery (黎陽郡; around present-day Xun County, Henan), where they stayed with Sima Lang's kinsman, Zhao Weisun. In 194, when war broke out between the warlords Cao Cao and Lü Bu, Sima Lang brought his family out of Liyang Commandery and again returned to their now-ravaged ancestral home in Wen County, Henei Commandery, where Sima Yi and his brothers largely sustained themselves by living as farmers; fending off local groups of bandits while studying diligently during their free time.: "是時董卓遷天子都長安，卓因留洛陽。朗父防為治書御史，當徙西，以四方雲擾，乃遣朗將家屬還本縣。 ...後數月，關東諸州郡起兵，衆數十萬，皆集熒陽及河內。諸將不能相一，縱兵鈔略，民人死者且半。久之，關東兵散，太祖與呂布相持於濮陽，朗乃將家還溫。"
Around 201, the administrative office of Henei Commandery nominated Sima Yi to serve in the government by holding local office, possibly as a clerk in charge of the records, and in 202 he was sent as a Reporting Officer () to the capital. notes: "Under the system of Han, heads of commandery units and provinces were required to present accounts to the court each New Year. The local officer sent to do so was known for that purpose as the Reporting Officer..." places this event one year earlier: "In the 6th Year of Han's Jian'an era ["Peacefulness Established", 201 AD], the commandery made him Reporting Officer [shangji yuan]." Around the same year, he married a woman named Zhang Chunhua, possibly at the instigation of his father. At the same time, the warlord Cao Cao, who then held the position of Minister of Works in the Han imperial court, heard of Sima Yi's talent and wanted to recruit him to serve in the administration. Sima Yi declined, presumably on grounds of illness, with the Book of Jin more specifically mentioning that he, seeing that the Han Empire's future was bleak, declined and lied by supposedly saying that he suffered from paralysis; staying at home, with Cao Cao's spies reporting that they saw Sima Yi lying motionless in bed.: "漢建安六年，郡舉上計掾。魏武帝為司空，聞而辟之。帝知漢運方微，不欲屈節曹氏，辭以風痺，不能起居。魏武使人夜往密刺之，帝堅卧不動。"
One day—in a story that may be apocryphal—while Sima Yi was drying his books under the sun, there was a sudden downpour, so he rushed out to grab his books and was seen by a maid. Sima Yi's wife, Zhang Chunhua, feared that the maid would leak out news that Sima Yi was well and get their family into trouble, so she killed the maid to silence her.: "宣帝初辭魏武之命，託以風痹，嘗暴書，遇暴雨，不覺自起收之。家惟有一婢見之，后乃恐事泄致禍，遂手殺之以滅口。"
Service under Cao Cao When Cao Cao died in Luoyang in March 220, there was apprehension in the imperial court. Sima Yi supervised the funerary arrangements to ensure everything would be carried out in an orderly fashion, places this responsibility on Sima Fu, his younger brother: "Sima Fu reprimanded them: 'Now the King is dead, we ought to pay our respects to his successor as early as possible, for the stabilization of the myriad states. Must we indulge in weeping only?' He then dismissed all of the officials from court, appointed palace guards, and attended to the business of the funeral. and accompanied the funeral cortège to Ye, earning the respect of officials within and outside the central government.: "及魏武薨于洛陽，朝野危懼。帝綱紀喪事，內外肅然。乃奉梓宮還鄴。"
Advising Cao Cao to attack Yi Province In 215, Sima Yi accompanied Cao Cao on his campaign against the warlord and Taoist religious leader Zhang Lu, whom Cao Cao defeated at the Battle of Yangping in Hanzhong Commandery. Afterwards Sima Yi urged him to capitalise on the momentum and attack his rival Liu Bei, who was in the neighboring Yi Province. Sima Yi said because Liu Bei had only recently seized control of Yi Province from Liu Zhang, he had yet to establish a strong foothold in the province. Cao Cao rejected Sima Yi's idea and said he was already content with having Longyou (; covering parts of present-day Gansu and Shaanxi)."Sima Yi, Master of Records to the Chancellor, said to Cao Cao, 'Liu Bei has captured Liu Zhang by deceit and force, and the people of Shu are not yet attached to him. Now that he is fighting far away in Jiangling, this is too good a chance to miss. You have conquered Hanzhong, and Yi province is trembling. Send your soldiers against them, and their position will disintegrate. The sage does not oppose the time, and he cannot let such opportunity slip.' 'A man who cannot be satisfied', remarked Cao Cao, 'will get Long and look to Shu.'"Translation . He then turned his attention to his other key rival Sun Quan.: "從討張魯，言於魏武曰：「劉備以詐力虜劉璋，蜀人未附而遠爭江陵，此機不可失也。今若曜威漢中，益州震動，進兵臨之，勢必瓦解。因此之勢，易為功力。聖人不能違時，亦不失時矣。」魏武曰：「人苦無足，既得隴右，復欲得蜀！」言竟不從。既而從討孫權，破之。"
Urging Cao Cao to usurp the throne